I'm not sure which Logic version you're using, on your screenshot it appears like you may use an older version with a customized GUI.
For reference, in Logic Pro 10.8.1. Control + S is assigned by default to Engage Solo Tracks (Channel Strips) of Selected Regions/Cells.
In earlier versions of Logic Pro that same shortcut was assigned to Toggle Region Solo (a.k.a. Solo Mode) which may have carried over if you were using an older Logic Pro version on your current Mac before updating to 10.8.1.
On your screenshot you are in Region Solo Lock Mode, which happens when you Control + click the Solo button in your Control bar and choose Solo Lock, or use a custom key command assignment for Set Solo Lock Mode.
In Solo Lock Mode, whatever regions were selected when you engaged Solo Lock remain soloed, no matter what you select afterwards.